Creates a SinkTIn, TMat that is materialized as an ISinkQueueT. PullAsync method is pulling element from the stream and returns TaskTResult. Task completes when element is available.

Before calling the pull method a second time you need to wait until previous future completes. Pull returns failed future with IllegalStateException if previous future has not yet completed.

SinkTIn, TMat will request at most number of elements equal to size of inputBuffer from upstream and then stop back pressure. You can configure size of input by using WithAttributes method.

For stream completion you need to pull all elements from ISinkQueueT including last None as completion marker.